Method of forming a lamination film pattern and improved lamination film pattern

ABSTRACT

In a method of forming an electrically conductive lamination pattern, an insulating film is formed on a surface of a chromium-containing bottom layer, before an aluminum-containing top layer is formed over the insulating film, so that the insulating film separates the aluminum-containing top layer from the chromium-containing bottom layer. A first selective wet etching process is carried out for selectively etching the aluminum-containing top layer with a first etchant. A second selective wet etching process is carried out for selectively etching the chromium-containing bottom layer with a second etchant in the presence the insulating film which suppresses a hetero-metal-contact-potential-difference between the chromium-containing bottom layer and the aluminum-containing top layer during the second selective wet etching process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of forming a lamination filmpattern and an improved lamination film pattern, and more particularlyto a method of forming a metal lamination film pattern which comprises afirst metal film comprising a refractory metal such as chromium or achromium alloy, and a second; metal film overlying the first metal filmand comprising aluminum or an aluminum alloy, wherein the method is freefrom any inhibition to etching for the first metal film of chromium orthe chromium alloy, and also free from any peeling of a resist film fromthe metal lamination film due to over-time etching process.

2. Description of the Related Art

All of patents, patent applications, patent publications, scientificarticles and the like, which will hereinafter be cited or identified inthe present application, will, hereby, be incorporated by references intheir entirety in order to describe more fully the state of the art, towhich the present invention pertains.

A liquid crystal display has a plurality of switching devices, each ofwhich comprises a thin film transistor (TFT), wherein any wiring delayappearing on a scanning line or a signal line causes a writing orcrosstalk problem. In order to avoid this problem, the liquid crystaldisplay, particularly to a large-scale and high-definition liquidcrystal display, uses a low-resistive wiring for the scanning line orthe signal line. In general, the low resistive wiring may comprisealuminum or an aluminum alloy. In the technical field of the liquidcrystal display, in order to ensure a desired ohmic contact with asemiconductor layer and a transparent conductive film. The low resistivewiring may comprise a lamination structure of an aluminum oraluminum-alloy film and a refractory metal film. Typically, for example,the low resistive wiring may, comprise a double-layered structure of analuminum layer and a refractory metal layer overlying the aluminumlayer. The low resistive wiring may also comprise another double-layeredstructure of a refractory metal layer and an aluminum layer overlyingthe refractory metal layer. The low resistive wiring may also comprise atriple-layered structure of a first refractory metal layer, an aluminumlayer overlying the first refractory metal layer, and a secondrefractory metal layer overlying the aluminum layer.

Japanese laid-open patent publication No. 4-155315 discloses aconventional method of forming an. Al/Cr lamination wiring, wherein analuminum film overlies a chromium film. This method is applied to a thinfilm transistor array substrate. FIGS. 1A through 1D are fragmentarycross sectional elevation views illustrative of an Al/Cr laminationwiring over a substrate in sequential steps involved in the conventionalmethod of forming the Al/Cr lamination wiring.

With reference to FIG. 1A, a first metal film 102 of chromium is formedover a substrate 101. A second metal film 103 of aluminum is then formedover the first metal film 102 of chromium, A desired resist pattern 104is formed over the second metal film 103 of aluminum. A first etchingprocess is taken place by using a first etchant and the resist pattern104 as an etching mask for selectively etching the second metal film 103of aluminum.

With reference to FIG. 1B, a second etching process is taken place byusing a second etchant and the resist pattern 104 as the etching maskfor selectively etching the first metal film 102 of chromium.

With reference to FIG. 1C, a third etching process as a side etchingprocess is taken place by using the first etchant and the resist pattern104 as the etching mask for selectively etching the side of the secondmetal film 103 of aluminum, so that the etched side edge of the secondmetal film 103 of aluminum is retracted by at least 0.5 micrometers fromthe side edge of the first metal film 102 of chromium.

With reference to FIG. 1D, the resist pattern 104 as used is thenremoved. Subsequently, a conductive film such as a pixel electrode isthen formed, which extends over the second metal film 103 of aluminumand the substrate 101.

The third etching process as the side etching process is taken place inorder to improve a step-coverage of the conductive film which extendsover the second metal film 103 of aluminum and the substrate 101,resulting in improves in the yield and the quality of the thin filmtransistor (TFT) substrate.

The present inventors had experimentally confirmed the fact that theabove-described conventional method of forming the lamination filmpattern has the following disadvantages.

The rate of the second etching process is extremely low due to aninhibition to the second etching process for the first metal film 102 ofchromium. Taking place the second etching process for a relatively longtime period causes that an etchant for the second etching process beinfiltrated into an interface between the resist pattern 104 and thesecond metal film 103 of aluminum, whereby the resist pattern 104 ispeeled to contaminate an etching apparatus.

The present inventors had also estimated that the reason for theinhibition to the second etching process for the first metal film 102 ofchromium is that a hetero-metal-contact-potential-difference between thefirst metal film 102 of chromium and the second metal film 103 ofaluminum causes the etchant for etching the first metal film 102 ofchromium to undesirably etch the second metal film 103 of aluminum.

In the above circumstances, the developments of a novel method offorming a lamination film pattern and of an improved lamination filmpattern free from the above problems are desirable.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novelmethod of forming a lamination film pattern free from the aboveproblems.

It is a further object of the present invention to provide a novelmethod of forming a lamination film pattern free from any inhibition tothe second etching process for a chromium containing film.

It is a still further object of the present invention to provide a novelmethod of forming a lamination film pattern free from any possiblepeeling phenomenon of the resist pattern due to any infiltration of theetchant on the ground of any over-time etching process for etching achromium containing film.

It is yet a further object of the present invention to provide a novellamination film pattern free from the above problems.

It is furthermore object of the present invention to provide a novellamination film pattern free from any inhibition to the second etchingprocess for a chromium containing film.

It is moreover object of the present invention to provide a novellamination film pattern free from free from any possible peelingphenomenon of the resist pattern due to any infiltration of the etchanton the ground of any over-time etching process for etching a chromiumcontaining film.

The present invention provides a method of forming an electricallyconductive lamination pattern. The method includes the steps of: formingan insulating film on a surface of a chromium-containing bottom layer;forming an aluminum-containing top layer over the insulating film, sothat the insulating film separates the aluminum-containing top layerfrom the chromium-containing bottom layer; carrying out a firstselective wet etching process for selectively etching thealuminum-containing top layer with a first etchant; and carrying out asecond selective wet etching process for selectively etching thechromium-containing bottom layer with a second etchant in the presencethe insulating film which suppresses ahetero-metal-contact-potential-difference between thechromium-containing bottom layer and the aluminum-containing top layerduring the second selective wet etching process.

The above and other objects, features and advantages of the presentinvention will be apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings.

FIGS. 1A through 1D are fragmentary cross sectional elevation viewsillustrative of an Al/Cr lamination wiring over a substrate insequential steps involved in the conventional method of forming theAl/Cr lamination wiring.

FIGS. 2A through 2G are fragmentary cross sectional elevation viewsillustrative of a novel method of forming a lamination film pattern inaccordance with the first embodiment of the present invention.

FIG. 3 is a schematic plan view illustrative of a thin film transistorsubstrate of a liquid crystal display.

FIG. 4 is a fragmentary plan view illustrative of a single pixelstructure of the thin film transistor substrate shown in FIG. 3.

FIGS. 5A through 5F are fragmentary cross sectional elevation viewsillustrative of a novel method of forming a thin film transistorsubstrate shown in FIGS. 3 and 4, taken along an A—A line of FIG. 4 anda B—B line of FIG. 3 as well as a C—C line of FIG. 3.

FIG. 6 is a fragmentary cross sectional elevation view illustrative of aliquid crystal display panel including in the thin film transistorsubstrate formed in the formation method shown in FIGS. 5A through 5F.

FIG. 7 shows the dependency of a tapered angle of a taperedaluminum-neodymium (Al—Nd) alloy film wet-etched by an etchant, uponconcentrations of nitric acid and acetic acid included in the etchant inaddition to 60 percents by weight of phosphoric acid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first aspect of the present invention provides a method of forming anelectrically conductive lamination pattern. The method includes thesteps of: forming an insulating film on a surface of achromium-containing bottom layer; forming an aluminum-containing toplayer over the insulating film, so that the insulating film separatesthe aluminum-containing top layer from the chromium-containing bottomlayer; carrying out a first selective wet etching process forselectively etching the aluminum-containing top layer with a firstetchant; and carrying out a second selective wet etching process forselectively etching the chromium-containing bottom layer with a secondetchant in the presence the insulating film which suppresses ahetero-metal-contact-potential-difference between thechromium-containing bottom layer and the aluminum-containing top layerduring the second selective wet etching process.

It is preferable that the first selective wet etching process is carriedout by using a resist pattern over the aluminum-containing top layer. Itis more preferable to further include the step of removing the resistpattern after the first selective wet etching process has beencompleted, so that the second selective wet etching process is carriedout by using, as a mask, the aluminum-containing top layer wet-etched inthe first selective wet etching process.

It is also preferable that the insulating film comprises an oxide filmformed by an oxidation process to the surface of the chromium-containingbottom layer. It is possible that the oxidation process to the surfaceof the chromium-containing bottom layer comprises an O₂ plasma process.Alternatively, it is possible that the oxidation process to the surfaceof the chromium-containing bottom layer comprises a reactive sputteringprocess. Further alternatively, it is also possible that the oxidationprocess to the surface of the chromium-containing bottom layer comprisesan anneal process.

It is also preferable that the insulating film has a thickness in therange of 5 nanometers to 50 nanometers.

It is also preferable that the first etchant comprises a mixture of aphosphoric acid, a nitric acid and an acetic acid, where a sum ofconcentrations of the nitric acid and the acetic acid is at least 16percents by weight.

It is also preferable to further include the step of carrying out aselective dry etching process, in addition to the second selective wetetching process, for selectively etching the chromium-containing bottomlayer. It is also preferable to further include the step of removing adry etching gas from a surface of the aluminum-containing top layerafter the selective dry etching process using the dry etching gas hasbeen completed.

It is also preferable that the chromium-containing bottom layercomprises one of a chromium layer and a chromium alloy layer, and thealuminum-containing top layer comprises one of an aluminum layer or analuminum alloy layer.

It is also preferable that the electrically conductive laminationpattern is formed over a substrate for a liquid crystal display panel.

A second aspect of the present invention provides a method of forming anelectrically conductive lamination pattern. The method includes thesteps of: forming a chromium-containing bottom layer over a substrate;forming an aluminum-containing top layer over the insulating film, sothat the insulating film separates the aluminum-containing top layerfrom the chromium-containing bottom layer; forming a resist pattern overthe aluminum-containing top layer; carrying out a first selective wetetching process for selectively etching the aluminum-containing toplayer with a first etchant and the resist pattern; removing the resistpattern from the aluminum-containing top layer; and carrying out asecond selective wet etching process for selectively etching thechromium-containing bottom layer with a second etchant and by using, asa mask, the aluminum-containing top layer wet-etched.

It is preferable that the first etchant comprises a mixture of aphosphoric acid, a nitric acid and an acetic acid, where a sum ofconcentrations of the nitric acid and the acetic acid is at least 16percents by weight.

It is also preferable to further include the step of forming aninsulating film on a surface of the chromium-containing bottom layerbefore the aluminum-containing top layer is then formed, so that thesecond selective wet etching process is carried out in the presence theinsulating film which suppresses ahetero-metal-contact-potential-difference between thechromium-containing bottom layer and the aluminum-containing top layerduring the second selective wet etching process. It is furtherpreferable that the insulating film comprises an oxide film formed by anoxidation process to the surface of the chromium-containing bottomlayer. It is further preferable that the oxidation process to thesurface of the chromium-containing bottom layer comprises an O₂ plasmaprocess.

It is also preferable that the oxidation process to the surface of thechromium-containing bottom layer comprises a reactive sputteringprocess.

It is also preferable that the oxidation process to the surface of thechromium-containing bottom layer comprises an anneal process.

It is also preferable that the insulating film has a thickness in therange of 5 nanometers to 50 nanometers.

It is also preferable to further include the step of carrying out aselective dry etching process, in addition to the second selective wetetching process, for selectively etching the chromium-containing bottomlayer. It is more preferable to further include the step of removing adry etching gas from a surface of the aluminum-containing top layerafter the selective dry etching process using the dry etching gas hasbeen completed.

It is also preferable that the chromium-containing bottom layercomprises one of a chromium layer and a chromium alloy layer, and thealuminum-containing top layer comprises one of an aluminum layer or analuminum alloy layer.

It is also preferable that the substrate is a thin film transistorsubstrate for a liquid crystal display.

A third aspect of the present invention provides an electricallyconductive lamination pattern structure including: a chromium-containingbottom layer; an insulating film extending over a surface of thechromium-containing bottom layer; and an aluminum-containing top layerextending over the insulating film, so that the insulating filmseparates the aluminum-containing top layer from the chromium-containingbottom layer.

It is also preferable that the aluminum-containing top layer is taperedin cross sectional elevation shape. It is more preferable that edges ofthe chromium-containing bottom layer and the insulating film are alignedto or positioned inside of a tapered edge of the aluminum-containing toplayer.

It is also preferable that the aluminum-containing top layer has a taperangle of at most approximately 60 degrees.

It is also preferable that the insulating film comprises an oxide filmformed by an oxidation process to the surface of the chromium-containingbottom layer.

It is also preferable that the insulating film has a thickness in therange of 5 nanometers to 50 nanometers.

It is also preferable that the chromium-containing bottom layercomprises one of a chromium layer and a chromium alloy layer, and thealuminum-containing top layer comprises one of an aluminum layer or analuminum alloy layer.

It is also preferable that the electrically conductive laminationpattern structure is formed over a substrate for a liquid crystaldisplay panel. It is also preferable that the substrate is a thin filmtransistor substrate for the liquid crystal display panel.

A fourth aspect of the present invention provides a thin film transistorsubstrate for a liquid crystal display panel, the thin film transistorsubstrate including at least one electrically conductive laminationpattern structure further including: a chromium-containing bottom layer;an insulating film extending over a surface of the chromium-containingbottom layer; and an aluminum-containing top layer extending over theinsulating film, so that the insulating film separates thealuminum-containing top layer from the chromium-containing bottom layer.

It is preferable that the aluminum-containing top layer is tapered incross sectional elevation shape. It is more preferable that edges of thechromium-containing bottom layer and the insulating film are aligned toor positioned inside of a tapered edge of the aluminum-containing toplayer.

It is also preferable that the aluminum-containing top layer has a taperangle of at most approximately 60 degrees.

It is also preferable that the insulating film comprises an oxide filmformed by an oxidation process to the surface of the chromium-containingbottom layer.

It is also preferable that the insulating film has a thickness in therange of 5 nanometers to 50 nanometers.

It is also preferable that the chromium-containing bottom layercomprises one of a chromium layer and a chromium alloy layer, and thealuminum-containing top layer comprises one of an aluminum layer or analuminum alloy layer.

The following embodiments are typical examples for practicing theforegoing aspects of the present invention. Although the subject mattersof the present invention have been described in details, the followingadditional descriptions in one or more typical preferred embodiments orexamples will be made with reference to the drawings for making it easyto understand the typical modes for practicing the foregoing aspects ofthe present invention.

First Embodiment

A first embodiment according to the present invention will be describedin detail with reference to the drawings. FIGS. 2A through 2G arefragmentary cross sectional elevation views illustrative of a novelmethod of forming a lamination film pattern in accordance with the firstembodiment of the present invention.

With reference to FIG. 2A, a first metal film 2 is formed over asubstrate 1. The first metal film 2 contains chromium. The first metalfilm 2 may, typically, comprise a chromium film or a chromium-alloyfilm, but should not be limited to these films. The first metal film 2may also typically have a thickness of approximately 70 nanometers. Thesubstrate 1 may include, but not limited to, a glass substrate and asemiconductor substrate. The method of forming the first metal film 2may include, but not limited to, a sputtering method by using asputtering system. In this case, the first metal film 2 is formed overthe substrate 1 in a sputter chamber of the sputtering system.

With reference to FIG. 2B, the substrate 1 with the first metal film 2is taken out from the sputter chamber, provided that the first metalfilm 2 was formed by the sputtering method. An insulating film 3 isformed on a surface of the first metal film 2. The insulating film 3 maypreferably comprise an oxide film. The oxide film 3 may typically have athickness preferably in the range of 5 nanometers to 50 nanometers, andmore preferably in the range of 10 nanometers to 50 nanometers. Theoxide film 3 may be formed by a surface oxidation to a surface of thefirst metal film 2. The surface oxidation may be available, for example,by using a reactive sputtering process, an O₂ plasma process, or ananneal. Notwithstanding, it is preferable for this embodiment that theoxide film 3 may be formed by the O₂ plasma process using a dry-etchapparatus configured in a plasma-etch-mode.

With reference to FIG. 2C, a second metal film 4 containing aluminum isformed on the insulating film 3 to form a lamination structure, whichincludes the first metal film 2, the insulating film 3, and the secondmetal film 4. The second metal film 4 is separated by the insulatingfilm 3 from the first metal film 2, so that aluminum of the second metalfilm 4 is separated from chromium of the first metal film 2, whereby thepresence of the insulating film 3 between the first metal film 2 and thesecond metal film 4 suppresses or reduces the above-described undesiredhetero-metal-contact-potential-difference between the first metal film 2and the second metal film 4. The second metal film 4 containing aluminummay, typically, comprise an aluminum film or an aluminum-alloy film, butshould not be limited to these films. The second metal film 4 may alsotypically have a thickness of approximately 300 nanometers.

As described above, the preferable thickness of the oxide film 3 is inthe range of 5 nanometers to 50 nanometers, and more preferably in therange of 10 nanometers to 50 nanometers. A much larger thickness than 50nanometers of the oxide film 3 is not preferable in a point of view suchthat the larger thickness makes it difficult to reduce a resistivity ofthe lamination structure. A much smaller thickness than 5 nanometers ofthe oxide film 3 is also not preferable in another point of view suchthat the smaller thickness allows a possible appearance of theabove-described undesired hetero-metal-contact-potential-differencebetween the first metal film 2 and the second metal film 4.

With reference to FIG. 2D, a resist film is applied on the second metalfilm 4 before lithography processes are then carried out so as toselectively form a resist mask 5 on the second metal film 4.

With reference to FIG. 2E, a first wet etching process is carried outfor etching the second metal film 4 by use of the resist mask 5 and afirst etchant. The first etchant may typically include a mixture of aphosphoric acid, an acetic acid and a nitric acid. The second metal film4 is selectively etched thereby to shape a tapered second metal film 4as well illustrated in this drawing. The tapered shape of the etchedsecond metal film 4 may be adjusted by an adjustment to a compositionalratio of the first etchant. It is, however, preferable for thecompositional ratio of the first etchant that the sum of bothconcentrations of the nitric acid and the acetic acid is at least 16percents by weight. One example of the compositional ratio of the firstetchant may be, but not limited to, that the etchant comprises 60percents by weight of the phosphoric acid, 12 percents by weight of theacetic acid, and 12 percents by weight of the nitric acid, and 16percents by weight of water.

With reference to FIG. 2F, the used resist mask 5 is removed after thefirst etching process for etching the second metal film 4 has beencompleted.

With reference to FIG. 2G, a second wet etching process is carried outfor selectively etching the insulating film 3, for example, the oxidefilm 3 and the first metal film 2 by use of the tapered second metalfilm 4 as a mask and a second etchant. The second etchant may typicallyinclude a mixture of ammonium cerium nitrate and an nitric acid. Theinsulating film 3 and the first metal film 2 are selectively etchedthereby to form a lamination film pattern, which comprises the etchedfirst metal film 2, the etched insulating film 3 and the taper-etchedsecond metal film 4 as well illustrated in FIG. 2G. It is preferable toavoid or possibly reduce any over-etching time of the second etchingprocess for the first metal film 2 in order to avoid or suppress thefirst metal film 2 from being side-etched with reference to the edges ofthe second metal film 4.

The presence of the insulating film 3 between the first metal film 2 andthe second metal film 4 suppresses or reduces the above-describedundesired hetero-metal-contact-potential-difference between the firstmetal film 2 and the second metal film 4, resulting in almost nosubstantive inhibition to the second wet etching process for the firstmetal film 2.

After the first etching process for etching the second metal film 4 hasbeen completed, the used resist mask 5 is then removed, before thesecond etching process for etching the insulating film 3 and the firstmetal film 2 will be made using the taper-etched second metal film 4 asthe mask. This does not cause that the resist mask 5 is peeled by anundesired infiltration of the second etchant into an interface betweenthe resist mask 5 and the second metal film 4 during the second etchingprocess for etching the insulating film 3 and the first metal film 2.

As described above, the surface oxidation to the first metal film 2 maypreferably be carried out by the O₂ plasma process. Examples ofpreferable conditions for carrying out the O₂ plasma process for thesurface oxidation to the first metal film 2 may be as follows:

-   Etching mode: plasma etching mode;-   Pressure: 133–260 (Pa);-   O₂ flow rate: approximately 400 (scam);-   Discharge power: 800–1500 (W); and-   Discharge time: approximately 60 seconds.

Examples of preferable conditions for carrying out the first wet etchingprocess for etching the second metal film 4 may be that the etching timeis ranged from at least 0.5 times to less than 1 time of the necessarytime for etching off an intended or targeted thickness for the etchingby using the first etchant as deteriorated at that time.

Examples of preferable conditions for carrying out the second wetetching process for etching the first metal film 2 may be that theetching time is ranged from approximately 2 or 3 times of the necessarytime for etching off an intended or targeted thickness for the etchingby using the second etchant as deteriorated at that time.

Instead of the O₂ plasma process as described above, the reactivesputtering process and the anneal process are also available as thesurface oxidation process for oxidizing the surface of the first metalfilm 2 containing chromium. The reactive sputtering process may becarried out by introducing O₂ gas in a predetermined final term of thesputtering process for forming the first metal film 2 containingchromium. The anneal may be carried out in the atmosphere. A naturaloxidation of merely exposing the surface of the first metal film 2 tothe atmosphere may result in a formation of an oxide film but which hasa smaller thickness than the lower limit of the preferable thicknessrange as described above. For this reason, the natural oxidation is notsuitable for forming the desired oxide film 3. A cleaning process and apeeling process are also may also result in a formation of an oxide filmbut which has a smaller thickness than the lower limit of the preferablethickness range as described above. For this reason, the cleaningprocess and the peeling process are also not suitable for forming thedesired oxide film 3.

The above-described second etching process may comprise the wet etchingprocess. Notwithstanding, the above-described second etching process mayalso comprise a combination of the wet etching process and a subsequentdry etching process. One typical example of the combined wet and dryetching processes will be described as follows.

A wet etching process as an initial etching process for isotropicallyetching the first metal film 2 containing chromium is carried out for ahalf-etching time ranged from approximately 1 or 1.5 times of thenecessary time for etching off an intended or targeted thickness for theetching by using the second etchant as deteriorated at that time,whereby approximately one half thickness of the first metal film 2 isisotropically etched.

A dry etching process as a subsequent etching process foranisotropically etching the remaining part of the first metal film 2containing chromium is carried out under the following conditions. Apressure is 40.0 Pa. Gas flow rates of Cl₂/O₂/He are 450/270/135 sccm. Adischarge power is 1600 W. A total discharge time of a just-etching timeand a subsequent over-etching time is 30 seconds.

An after-corrosion process is then carried out following to thelast-described dry etching process, for the purpose of removing achorine gas as adhered on the surface of the second metal film 4containing aluminum during the last-mentioned dry etching process forthe first metal film 2 containing chromium, thereby avoiding anyundesired formation of a hydrochloric acid through a chemical reactionof the adhered chorine gas with a moisture of the air when the substrateis taken out from a dry etching chamber. The avoidance to the formationof the hydrochloric acid prevents any corrosion of the second metal film4 containing aluminum.

The after-corrosion process may typically comprise the following firstand second steps under different conditions.

The conditions for the first step are that the pressure is 6.67 Pa, thegas flow rates of CF₄/O₂ are 110/990 sccm, the discharge power is 0 W,and the discharge time is 70 seconds.

The conditions for the second step are that the pressure is 6.67 Pa, thegas flow rates of CF₄/O₂ are 80/720 sccm, the discharge power is 1000 W,and the discharge time is 60 seconds.

As described above, the presence of the insulating film 3 between thefirst metal film 2 and the second metal film 4 suppresses or reduces theabove-described undesired hetero-metal-contact-potential-differencebetween the first metal film 2 and the second metal film 4, resulting inalmost no substantive inhibition to the second wet etching process forthe first metal film 2. After the first etching process for etching thesecond metal film 4 has been completed, the used resist mask 5 is thenremoved, before the second etching process for etching the insulatingfilm 3 and the first metal film 2 will be made using the taper-etchedsecond metal film 4 as the mask. This does not cause that the resistmask 5 is peeled by an undesired infiltration of the second etchant intoan interface between the resist mask 5 and the second metal film 4during the second etching process for etching the insulating film 3 andthe first metal film 2.

The above-described novel method of forming the lamination film patternin accordance with the present invention may be applicable to anydevices which include at least one of such lamination film pattern.Typical examples of such the lamination film pattern may include, butnot limited to, a gate electrode, a scanning line, source and drainelectrodes and a signal line over a thin film transistor substrate of aliquid crystal display.

FIG. 3 is a schematic plan view illustrative of a thin film transistorsubstrate of a liquid crystal display. A thin film transistor substrate10 comprises a transparent insulating substrate, over which a pluralityof scanning lines 11 run in a first horizontal direction and a pluralityof signal lines 12 run in a second horizontal direction which mayapproximately be perpendicular to the first horizontal direction. Theplurality of scanning lines 11 cross the plurality of signal lines 12 atapproximately the right angle. A matrix array of plural switchingdevices are provided over the thin film transistor substrate 10, whereinthe plurality of switching devices are positioned adjacent to crossingpoints of the plurality of scanning lines 11 and the plurality of signallines 12. The plurality of switching devices are electrically connectedto the plurality of scanning lines 11 and also electrically connected tothe plurality of signal lines 12. Each of the plurality of switchingdevices may typically comprise a thin film transistor 13. Scanning lineterminals 14 are provided at terminals of the scanning lines 11. Addresssignals are inputted into the scanning line terminals 14. Signal lineterminals 15 are provided at terminals of the signal lines 12. Datasignals are inputted into the signal line terminals 15, A matrix arrayof pixel electrodes are also provided over the thin film transistorsubstrate 10. A drain electrode of the thin film transistor 13 iselectrically connected to the signal line 12. A gate electrode of thethin film transistor 13 is electrically connected to the scanning line11. A source electrode of the thin film transistor 13 is electricallyconnected to the pixel electrode.

FIG. 4 is a fragmentary plan view illustrative of a single pixelstructure of the thin film transistor substrate shown in FIG. 3. FIGS.5A through 5F are fragmentary cross sectional elevation viewsillustrative of a novel method of forming a thin film transistorsubstrate shown in FIGS. 3 and 4, taken along an A—A line of FIG. 4 anda B—B line of FIG. 3 as well as a C—C line of FIG. 3. FIG. 6 is afragmentary cross sectional elevation view illustrative of a liquidcrystal display panel including in the thin film transistor substrateformed in the formation method shown in FIGS. 5A through 5F.

In accordance with this embodiment, the thin film transistor substratecomprises a reverse-staggered channel-etched thin film transistor whichmay be fabricated by using six masks.

With reference to FIGS. 4 and 5F, each pixel structure is formed over atransparent insulating substrate 20. The each pixel structure is definedby a first pair of adjacent two of the scanning lines 11 and a secondpair of adjacent two of the signal lines 12. The each pixel structureincludes a pixel electrode 21, a gate electrode 22 connected to thescanning line 11, a gate insulating film 23 overlying the gate electrode22 and the scanning line 11, a semiconductor layered structure 24 overthe gate insulating film 23, and source and drain electrodes 25 and 26partly over the semiconductor layered structure 24 as well as a storagecapacitor electrode 34 and a pair of optical shielding layers 35. Thesource and drain electrodes 25 and 26 are separated from each other. Apixel contact hole 31 is formed over the pixel electrode 21. Terminalcontact holes 32 are formed over the signal line terminal 15 and thescanning line terminal 14. A storage capacitor electrode contact hole 33is also formed over the storage capacitor electrode 34. The signal line12 extends over the gate insulating film 23. The signal line 12 isconnected with the drain electrode 26. The storage capacitor electrode34 is connected through the storage capacitor electrode contact hole 33to the scanning line 11 on the previous stage. The thin film transistorcomprises the gate electrode 22, the source electrode 25 and the drainelectrode 26. Passivation films 27 extend over the thin film transistorand the optical shielding layers 35. Openings 36 are formed in the gateinsulating film 23 and the passivation film 27, wherein the openings 36extend inside the pixel contact hole 31 and the terminal contact holes32. The source electrode 25 is electrically connected to the pixelelectrode 21 through the pixel contact hole 31. The signal line terminal15 is electrically connected to the terminal of the signal line 12through the terminal contact hole 32. The storage capacitor electrode 34and the pixel electrode 21 form a capacitor which is illustrated in FIG.3.

The following descriptions with reference to FIGS. 5A through 5F andFIG. 6 will focus on a method of fabricating a liquid crystal displayincluding a thin film transistor substrate, to which the method offorming the lamination film pattern is applied in accordance with thepresent invention.

The method of forming the thin film transistor substrate includes thefollowing six steps. The first step is to form a pixel electrode over atransparent insulating substrate. The second step is to form a gateelectrode and a scanning electrode. The third step is to form a gateinsulating film and a semiconductor layered structure. The fourth stepis to form contact holes. The fifth step is to form source and drainelectrodes and a signal line. The sixth step is to form a passivationfilm and openings.

Each of the gate electrode, the scanning line, the source and drainelectrodes and the signal line comprises a double-layered laminationpattern of a chromium-containing bottom layer and an aluminum-containingtop layer, wherein an oxide layer is formed on a surface of thechromium-containing bottom layer, so that the aluminum-containing toplayer is separated from the chromium-containing bottom layer by theoxide layer.

The aluminum-containing top layer is selectively etched by using aresist mask, and then the resist mask is removed before thechromium-containing bottom layer is selectively etched by using theselectively etched aluminum-containing top layer as a mask, thereby toform a double-layered lamination pattern.

With reference to FIG. 5A, a transparent conductive film is formed overa transparent insulating substrate 20 by a sputtering method. Thetransparent insulating substrate 20 may typically comprise a non-alkaliglass having a thickness of 0.7 millimeters. The transparent conductivefilm may have a thickness of 50 nanometers. The transparent conductivefilm may typically comprise either an indium tin oxide film or an indiumzinc oxide film. The transparent conductive film is then subjected to alithography process and a subsequent selective etching process forpatterning the transparent conductive film, thereby to make thetransparent conductive film into a pixel electrode 21, a scanningelectrode terminal 14 and a signal electrode terminal 15.

With reference to FIG. 5B, a chromium-containing bottom layer is formed,by a sputtering method, over the transparent insulating substrate 20 aswell as over the pixel electrode 21, the scanning electrode terminal 14and the signal electrode terminal 15. The chromium-containing bottomlayer may typically comprise either a chromium layer or a chromium-alloylayer. The chromium-containing bottom layer may typically have athickness of approximately 70 nanometers. Preferable examples of thechromium alloy layer may include, but not limited to, a chromiummolybdenum layer or a chromium nitride layer.

The transparent insulating substrate 20 is then taken out from thesputter chamber. An insulating film is formed on a surface of thechromium-containing bottom layer. The insulating film may preferablycomprise an oxide film. The oxide film may typically have a thicknesspreferably in the range of 5 nanometers to 50 nanometers, and morepreferably in the range of 10 nanometers to 50 nanometers. The oxidefilm may be formed by a surface oxidation to a surface of thechromium-containing bottom layer. The surface oxidation may beavailable, for example, by using a reactive sputtering process, an O₂plasma process, or an anneal. Notwithstanding, it is preferable for thisembodiment that the oxide film may be formed by the O₂ plasma processusing a dry-etch apparatus configured in a plasma-etch-mode.

An aluminum-containing top layer is formed, by a sputtering method, overthe oxide film on the surface of the chromium-containing bottom layer,whereby a lamination structure is formed, which comprises adouble-layered structure of the chromium-containing bottom layer and thealuminum-containing top layer, both of which are separated by the oxidefilm formed on the surface of the chromium-containing bottom layer. Thealuminum-containing top layer may typically have a thickness ofapproximately 300 nanometers. The aluminum-containing top layer maytypically comprise either an aluminum layer or an aluminum alloy layer.Preferable examples of the aluminum alloy layer may include, but notlimited to, an aluminum-copper layer and an aluminum-neodymium.

The lamination structure is then subjected to a lithography process anda subsequent selective etching process for patterning the laminationstructure, thereby to make the lamination structure into a gateelectrode 22 and a scanning line not illustrated in FIG. 5B. Thelithography process and the subsequent selective etching process are asfollows.

A resist film is applied on the aluminum-containing top layer beforelithography processes are then carried out so as to selectively form aresist mask on the aluminum-containing top layer.

A first wet etching process is carried out for etching thealuminum-containing top layer by use of the resist mask and a firstetchant. The first etchant may typically include a mixture of aphosphoric acid, an acetic acid and a nitric acid. Thealuminum-containing top layer is selectively etched thereby to shape atapered aluminum-containing top layer, The tapered shape of the etchedaluminum-containing top layer may be adjusted by an adjustment to acompositional ratio of the first etchant. It is, however, preferable forthe compositional ratio of the first etchant that the sum of bothconcentrations of the nitric acid and the acetic acid is at least 16percents by weight. One example of the compositional ratio of the firstetchant may be, but not limited to, that the etchant comprises 60percents by weight of the phosphoric acid, 12 percents by weight of theacetic acid, and 12 percents by weight of the nitric acid, and 16percents by weight of water.

The used resist mask is removed after the first etching process foretching the aluminum-containing top layer has been completed.

A second wet etching process is carried out for selectively etching theoxide film and the chromium-containing bottom layer by use of thetapered aluminum-containing top layer as a mask and a second etchant.The second etchant may typically include a mixture of ammonium ceriumnitrate and a nitric acid. The oxide film and the chromium-containingbottom layer are selectively etched thereby to form the gate electrode22 and the scanning line which comprise lamination film patterns, eachof which comprises the etched chromium-containing bottom layer, theetched oxide film and the taper-etched aluminum-containing top layer. Itis preferable to avoid or possibly reduce any over-etching time of thesecond etching process for the chromium-containing bottom layer in orderto avoid or suppress the chromium-containing bottom layer from beingside-etched with reference to the edges of the taper-etchedaluminum-containing top layer.

The presence of the oxide film between the chromium-containing bottomlayer and the aluminum-containing top layer suppresses or reduces theabove-described undesired hetero-metal-contact-potential-differencebetween the chromium-containing bottom layer and the aluminum-containingtop layer, resulting in almost no substantive inhibition to the secondwet etching process for the chromium-containing bottom layer.

After the first etching process for etching the aluminum-containing toplayer has been completed, the used resist mask is then removed, beforethe second etching process for etching the oxide film and thechromium-containing bottom layer will be made using the taper-etchedaluminum-containing top layer as the mask. This does not cause that theresist mask is peeled by an undesired infiltration of the second etchantinto an interface between the resist mask and the aluminum-containingtop layer during the second etching process for etching the oxide filmand the chromium-containing bottom layer.

With reference to FIG. 5C, a gate insulating film 23 is entirely formed,by a plasma enhanced chemical vapor deposition method, over thetransparent insulating substrate 20, the gate electrode 22, the pixelelectrode 21, the signal line terminal 15, the scanning line terminal 14and the scanning line. The gate insulating film 23 may typicallycomprise a silicon nitride film. The gate insulating film 23 maytypically have a thickness of approximately 400 nanometers. An undopedamorphous silicon layer 28 is also formed, by a plasma enhanced chemicalvapor deposition method, over the gate insulating film 23. The undopedamorphous silicon layer 28 may typically have a thickness ofapproximately 200 nanometers. A phosphorous-doped amorphous siliconlayer 29 is also formed, by a plasma enhanced chemical vapor depositionmethod, over the undoped amorphous silicon layer 28, thereby to form adouble-layered amorphous silicon structure. The double-layered amorphoussilicon structure is then subjected to a lithography process and asubsequent etching process for patterning the double-layered amorphoussilicon structure, thereby making the double-layered amorphous siliconstructure into a semiconductor layer 24. The semiconductor layer 24extends over the gate insulating film 23 and is positioned over the gateelectrode 22.

With reference to FIG. 5D, a pixel contact hole 31, terminal contactholes 32 and a storage capacitor electrode contact hole 33 are formed inthe gate insulating film 23. The pixel contact hole 31 is positionedover the pixel electrode 21. The terminal contact holes 32 arepositioned over the canning line terminal 14 and the signal lineterminal 15. The storage capacitor electrode contact hole 33 ispositioned over the scanning line 11.

With reference to FIG. 5E, a source electrode 25, a drain electrode 26and a signal line 12 are formed in the same processes as described abovein accordance with the present invention. Namely, a chromium-containingbottom layer is formed, by a sputtering method, over the semiconductorlayer 24 and the gate insulating film 23 as well as over the pixelcontact hole 31, the terminal contact holes 32 and the storage capacitorelectrode contact hole 33. The chromium-containing bottom layer maytypically comprise either a chromium layer or a chromium-alloy layer.The chromium-containing bottom layer may typically have a thickness ofapproximately 70 nanometers. Preferable examples of the chromium alloylayer may include, but not limited to, a chromium molybdenum layer or achromium nitride layer.

The transparent insulating substrate 20 is then taken out from thesputter chamber. An insulating film is formed on a surface of thechromium-containing bottom layer. The insulating film may preferablycomprise an oxide film. The oxide film may typically have a thicknesspreferably in the range of 5 nanometers to 50 nanometers, and morepreferably in the range of 10 nanometers to 50 nanometers. The oxidefilm may be formed by a surface oxidation to a surface of thechromium-containing bottom layer. The surface oxidation may beavailable, for example, by using a reactive sputtering process, an O₂plasma process, or an anneal. Notwithstanding, it is preferable for thisembodiment that the oxide film may be formed by the O₂ plasma processusing a dry-etch apparatus configured in a plasma-etch-mode.

An aluminum-containing top layer is formed, by a sputtering method, overthe oxide film on the surface of the chromium-containing bottom layer,whereby a lamination structure is formed, which comprises adouble-layered structure of the chromium-containing bottom layer and thealuminum-containing top layer, both of which are separated by the oxidefilm formed on the surface of the chromium-containing bottom layer. Thealuminum-containing top layer may typically have a thickness ofapproximately 200 nanometers. The aluminum-containing top layer maytypically comprise either an aluminum layer or an aluminum alloy layer.Preferable examples of the aluminum alloy layer may include, but notlimited to, an aluminum-copper layer and an aluminum-neodymium.

The lamination structure is then subjected to a lithography process anda subsequent selective etching process for patterning the laminationstructure, thereby to make the lamination structure into a sourceelectrode 25, a drain electrode 26 and a signal electrode 12. Thelithography process and the subsequent selective etching process are asfollows.

A resist film is applied on the aluminum-containing top layer beforelithography processes are then carried out so as to selectively form aresist mask on the aluminum-containing top layer.

A first wet etching process is carried out for etching thealuminum-containing top layer by use of the resist mask and a firstetchant. The first etchant may typically include a mixture of aphosphoric acid, an acetic acid and a nitric acid. Thealuminum-containing top layer is selectively etched thereby to shape atapered aluminum-containing top layer. The tapered shape of the etchedaluminum-containing top layer may be adjusted by an adjustment to acompositional ratio of the first etchant. It is, however, preferable forthe compositional ratio of the first etchant that the sum of bothconcentrations of the nitric acid and the acetic acid is at least 16percents by weight. One example of the compositional ratio of the firstetchant may be, but not limited to, that the etchant comprises 60percents by weight of the phosphoric acid, 12 percents by weight of theacetic acid, and 12 percents by weight of the nitric acid, and 16percents by weight of water.

The used resist mask is removed after the first etching process foretching the aluminum-containing top layer has been completed.

A second wet etching process is carried out for selectively etching theoxide film and the chromium-containing bottom layer by use of thetapered aluminum-containing top layer as a mask and a second etchant.The second etchant may typically include a mixture of ammonium ceriumnitrate and a nitric acid. The oxide film and the chromium-containingbottom layer are selectively etched thereby to form the gate electrode22 and the scanning line which comprise lamination film patterns, eachof which comprises the etched chromium-containing bottom layer, theetched oxide film and the taper-etched aluminum-containing top layer. Itis preferable to avoid or possibly reduce any over-etching time of thesecond etching process for the chromium-containing bottom layer in orderto avoid or suppress the chromium-containing bottom layer from beingside-etched with reference to the edges of the taper-etchedaluminum-containing top layer.

The second wet etching process may be carried out in combination with adry etching process. It is, however, preferable as described above, thesecond wet etching process may be carried out solely because anafter-corrosion process subsequent to the dry etching process mayprovide a damage to the semiconductor layer 24 and the gate insulatingfilm 23.

In order to avoid or prevent any corrosion of the aluminum-containingtop layer due to an etching gas in a later process for forming achannel, it is preferable that either after the first wet etchingprocess for the aluminum-containing top layer has been completed orafter the resist mask has been removed, then a water cleaning process iscarried out using a hot water of a temperature in the range ofapproximately 40° C. to approximately 50° C., and further a protectionfilm is formed on the upper surface and the side faces of thealuminum-containing top layer. The protection film may typicallycomprise either an oxide film or a hydroxide film. A preferablethickness of the protection film may depend upon a temperature of thehot water. A typical example of the preferable thickness of theprotection film may be ranged from 200 nanometers to 300 nanometers.

The presence of the oxide film between the chromium-containing bottomlayer and the aluminum-containing top layer suppresses or reduces theabove-described undesired hetero-metal-contact-potential-differencebetween the chromium-containing bottom layer and the aluminum-containingtop layer, resulting in almost no substantive inhibition to the secondwet etching process for the chromium-containing bottom layer.

After the first etching process for etching the aluminum-containing toplayer has been completed, the used resist mask is then removed, beforethe second etching process for etching the oxide film and thechromium-containing bottom layer will be made using the taper-etchedaluminum-containing top layer as the mask. This does not cause that theresist mask is peeled by an undesired infiltration of the second etchantinto an interface between the resist mask and the aluminum-containingtop layer during the second etching process for etching the oxide filmand the chromium-containing bottom layer.

With still reference to FIG. 5E, a part of the phosphorous-dopedamorphous silicon layer 29 exposed through a gap between the sourceelectrode 25 and the drain electrode 26 is then etched by an etchingprocess. This etching process may typically comprise a dry etchingprocess. Typical examples of the dry etching process may include, butnot limited to, a plasma etching process and a reactive ion etchingprocess. In each of the plasma etching process and the reactive ionetching process, typical examples of the etching gas may include, butnot limited to, fluorine-containing gases used solely, or in combinationwith chlorine-containing gases which exclude a pure chlorine gas. Forexample, there is available nother mixture gas of sulfur hexafluoride(SF₆), hydrochloric acid (HCl) and helium (He). In two-steps etchingprocess, there is available a mixture gas of methane trifluoride (CHF₃),oxygen (O₂) and helium (He) used in combination with the above-describedmixture gas of sulfur hexafluoride (SF₆), hydrochloric acid (HCl) andhelium (He). In two-steps etching process, there is also available theabove-described mixture gas of methane trifluoride (CHF₃), oxygen (O₂)and helium (He) used in combination with still another mixture gas ofsulfur hexafluoride (SF₆), methane trifluoride (CHF₃) and helium (He).The reason why the pure chlorine gas is excluded is to suppress thecorrosion of the aluminum-containing top layer.

The presence of the above-described protection layer over thealuminum-containing top layer prevents the aluminum-containing top layerfrom exposure to a plasma of the above-described etching gas.

After the above-described dry etching process has been made, then thedry etching chamber is vacuumed, wherein the substrate 20 is preferablyseparated from the electrode, so as to remove any etching gases adheredon a bottom surface of the substrate.

After the vacuum process has been made, then some residues of fluorineand chlorine might be presented in the vacuumed chamber. A plasmaprocess is carried out in the vacuumed chamber by using either gas ofoxygen (O₂), nitrogen (N₂), hydrogen (H₂) and helium (He), whereby theplasma process substitutes the residues of fluorine and chlorine. If theresidues of fluorine and chlorine are not removed from the surface ofthe substrate 20, while the substrate 20 is carried to or exposed to anatmosphere, then the residues of fluorine and chlorine on the substrate20 show a chemical reaction with moisture of the atmosphere, therebyforming hydrofluoric acid (HF) and hydrochloric acid (HCl), resulting ina corrosion of the aluminum-containing top layer. The above-describedmethod in accordance with the present invention prevents thealuminum-containing top layer from exposure to the plasma gas acting asthe etching gas, and also remove the residues of fluorine and chlorineon the substrate 20, resulting in no corrosion of thealuminum-containing top layer.

With reference to FIG. 5F, a passivation film 27 is entirely formed, bya plasma enhanced chemical vapor deposition method, over the sourceelectrode 25, the drain electrode 26, the signal line 12, the scanningline 11, the pixel electrode 21, the signal line terminal 15, thescanning line terminal 14, the gate insulating film 23 and a part of theundoped amorphous silicon layer 28. The passivation film 27 maytypically comprise a silicon nitride film. A typical thickness of thepassivation film 27 my be, but not limited to, approximately 200nanometers. The passivation film 27 is then subjected to a lithographyprocess and a subsequent etching process, to form openings 36 over thepixel electrode 21, the signal line terminal 15, and the scanning lineterminal 14. Finally, an anneal is made at a temperature ofapproximately 270° C. to complete the thin film transistor substrate.

The insulating layer, typically the oxide layer, formed on the surfaceof the chromium-containing bottom layer may preferably be so thin as tohave a thickness ranged from 5 nanometers to 50 nanometers. Further,address signals and data signals are generated by AC-drive. Alternatingcurrents as the address signals and data signals flow both thealuminum-containing top layer and the chromium-containing bottom layer.

Even if the above-described counter-measure is not made to suppress thechromium-containing bottom layer from being side-etched with referenceto the edges of the taper-etched aluminum-containing top layer, thenboth the tapered-shape of the etched aluminum-containing top layer andthe thicker thickness of the aluminum-containing top layer than thechromium-containing bottom layer cause no problem with coverage of theoverlying gate insulating film and the overlying passivation film.

The following descriptions with reference to FIG. 6 will focus on thesubsequent processes for forming the liquid crystal display from thethin film transistor substrate.

A first orientation film 41 is formed, by a printing method, over theabove-described thin film transistor substrate 10. A typical thicknessof the first orientation film 41 may be, but not limited to,approximately 50 nanometers. The first orientation film 41 is thensintered or baked at approximately 220° C. A first orientation processis carried out to the first orientation film 41, so that the firstorientation film 41 has a first orientation.

An opposite substrate 40 is formed, which faces to the above-describedthin film transistor substrate 10. The opposite substrate 40 includes atransparent insulating substrate 50, a color filter 42, a black matrix43 and a common electrode 44. The transparent insulating substrate 50may typically comprise, but not limited to, a non-alkali glass having athickness of 0.7 millimeters. The color filter 42, the black matrix 43and the common electrode 44 are formed over the transparent insulatingsubstrate 50. The color filter 42 of the opposite substrate 40 is soaligned, in the plan view, as corresponding to the thin film transistor13 of the thin film transistor substrate 10. The black matrix 43 is soaligned, in the plan view, as corresponding to a peripheral region of apixel region which includes the thin film transistor 13. The commonelectrode 44 covers the color filter 42 and the black matrix 43, whichare formed on the surface of the transparent insulating substrate 50.The common electrode 44 may typically comprise a transparent conductivefilm such as indium tin oxide. As a top layer of the opposite substrate40, a second orientation film 41 is formed by a printing method, whichcovers the common electrode 44. A typical thickness of the secondorientation film 41 may be, but not limited to, 50 nanometers. Thesecond orientation film 41 is then sintered or baked at a temperature ofapproximately 220° C. The thin film transistor substrate 10 and theopposite substrate 40 are combined with other through a seal 45 and anin-plane spacer not illustrated, so that the first orientation film 41of the thin film transistor substrate 10 faces to the second orientationfilm 41 of the opposite substrate 40, and also that the thin filmtransistor substrate 10 and the opposite substrate 40 are distanced fromeach other to form an inter-space defined between the thin filmtransistor substrate 10 and the opposite substrate 40. The seal 45 maytypically comprise, but not limited to, an epoxy resin adhesive. Thein-plane spacer may typically comprise, but not limited to, particles ofa plastic.

A liquid crystal 46 is injected into the inter-space defined between thethin film transistor substrate 10 and the opposite substrate 40. Anopening of the seal 45, form which the liquid crystal 46 has beeninjected, is then sealed with a sealing agent. The sealing agent maytypically comprise, but not limited to, an UV-thermosetting acrylateresin. First and second polarization plates 47 are adhered to outersurfaces of the transparent insulating substrates 20 and 50, therebycompleting a liquid crystal panel.

A tape carrier package (TCP) for connection to a driver circuit ispressure-welded to the scanning line terminal 14 and the signal lineterminal 15, thereby completing a liquid crystal display.

The following descriptions will focus on a composition of theabove-described first etchant used in the above-described first etchingprocess for etching the aluminum-containing top layer laminated on theinsulating film or the oxide film on the surface of thechromium-containing bottom layer. FIG. 7 shows the dependency of a taperangle of a tapered aluminum-neodymium (Al—Nd) alloy film wet-etched byan etchant, upon concentrations of nitric acid and acetic acid includedin the etchant in addition to 60 percents by weight of phosphoric acid.The tapered angle is defined to be “θ” shown in FIG. 2G. A mark “∘”represents that the taper angle “θ” is approximately 30 degrees. Anothermark “□” represents that the taper angle “θ” is approximately 45degrees. Still another mark “Δ” represents that the taper angle “θ” isapproximately 60 degrees. Yet another mark “ ” represents that the taperangle “θ” is ranged approximately 80 degrees to approximately 90degrees. FIG. 7 demonstrates that if the sum of both the concentrationsof nitric acid and acetic acid is at least 16 percents by weight, thenthe taper angle is at most approximately 60 degrees. The dependency,shown in FIG. 7, of the taper angle upon both the concentrations ofnitric acid and acetic acid is independent from the concentration ofphosphoric acid. It was also confirmed that almost the same dependenciesas shown in FIG. 7 of the taper angle upon both the concentrations ofnitric acid and acetic acid are established at different phosphoric acidconcentrations of 70 percents by weight, 60 percents by weight and 40percents by weight. The concentration of phosphoric acid provides asubstantive influence only to the etching rate of etching thealuminum-containing top layer, but no influence to the taper angle ofthe etched aluminum-containing top layer.

Nitric acid acts to reduce an adhesiveness between the resist patternand the aluminum-containing top layer. The increase in the concentrationof nitric acid decreases the taper angle of the etchedaluminum-containing top layer. Acetic acid is added into the etchant asa buffer. Notwithstanding, acetic acid also acts to reduce theadhesiveness between the resist pattern and the aluminum-containing toplayer. The increase in the concentration of acetic acid decreases thetaper angle of the etched aluminum-containing top layer.

Consequently, if the sum of both the concentrations of nitric acid andacetic acid included together with phosphoric acid in the first etchantused for wet-etching the aluminum-containing top layer is at least 16percents by weight, then the desired taper angle of the etchedaluminum-containing top layer is obtained.

In accordance with the present invention, as described above, thepresence of the insulating film 3, for example, the oxide film betweenthe first metal film 2, for example, the chromium-containing bottomlayer and the second metal film 4, for example, the aluminum-containingtop layer suppresses or reduces the above-described undesiredhetero-metal-contact-potential-difference between the first metal film2, for example, the chromium-containing bottom layer and the secondmetal film 4, for example, the aluminum-containing top layer, resultingin almost no substantive inhibition to the second wet etching processfor the first metal film 2, for example, the chromium-containing bottomlayer.

After the first etching process for etching the second metal film 4 hasbeen completed, the used resist mask 5 is then removed, before thesecond etching process for etching the insulating film 3, for example,the oxide film and the first metal film 2 will be made using thetaper-etched second metal film 4 as the mask. This does not cause thatthe resist mask 5 is peeled by an undesired infiltration of the secondetchant into an interface between the resist mask 5 and the second metalfilm 4 during the second etching process for etching the insulating film3 and the first metal film 2.

It is preferable that the sum of both the concentrations of nitric acidand acetic acid included together with phosphoric acid in the firstetchant used for wet-etching the aluminum-containing top layer is atleast 16 percents by weight, then the desired taper angle of the etchedaluminum-containing top layer is obtained.

In accordance with the above-described embodiment, the thin filmtransistor of the liquid crystal display has the reverse-staggered thinfilm transistor. The above-described novel method of forming thelamination film pattern is applied to the gate electrode, the scanningline, the source electrode, the drain electrode, and the signal line.Notwithstanding, typical examples, to which the above-described novelmethod of forming the lamination film pattern is also applicable, mayinclude, but not limited to, the gate electrode and the scanning line ofa forward-staggered thin film transistor as well as reflectingelectrodes of reflective or semi-transmitting liquid crystal display.Typical examples of the switching device may include, but not limitedto, a polysilicon thin film transistor and a metal-insulator-metaltransistor. The lamination film structure of the chromium-containingbottom layer and the aluminum-containing top layer may be used toimprove an ohmic contact with an underlying transparent conductive filmand an underlying metal film which extend under the lamination filmstructure.

Typical examples of the resist pattern may include a photo-resistpattern, an X-ray resist pattern and an electron beam resist pattern.

Although the invention has been described above in connection withseveral preferred embodiments therefor, it will be appreciated thatthose embodiments have been provided solely for illustrating theinvention, and not in a limiting sense. Numerous modifications andsubstitutions of equivalent materials and techniques will be readilyapparent to those skilled in the art after reading the presentapplication, and all such modifications and substitutions are expresslyunderstood to fall within the true scope and spirit of the appendedclaims.

1. A method of forming an electrically conductive lamination pattern,said method including the steps of: forming an insulating film on asurface of a chromium-containing bottom layer; forming analuminum-containing top layer over said insulating film, so that saidinsulating film separates said aluminum-containing top layer from saidchromium-containing bottom layer; carrying out a first selective wetetching process for selectively etching said aluminum-containing toplayer with a first etchant; and carrying out a second selective wetetching process for selectively etching said chromium-containing bottomlayer with a second etchant in the presence of said insulating filmwhich suppresses a hetero-metal-contact-potential-difference betweensaid chromium-containing bottom layer and said aluminum-containing toplayer during said second selective wet etching process.
 2. The method asclaimed in claim 1, wherein said first selective wet etching process iscarried out by using a resist pattern over said aluminum-containing toplayer.
 3. The method as claimed in claim 2, further including the stepof removing said resist pattern after said first selective wet etchingprocess has been completed, so that said second selective wet etchingprocess is carried out by using, as a mask, said aluminum-containing toplayer wet-etched in said first selective wet etching process.
 4. Themethod as claimed in claim 1, wherein said insulating film comprises anoxide film formed by an oxidation process to said surface of saidchromium-containing bottom layer.
 5. The method as claimed in claim 4,wherein said oxidation process to said surface of said chromiumcontaining bottom layer comprises an O₂ plasma process.
 6. The method asclaimed in claim 4, wherein said oxidation process to said surface ofsaid chromium-containing bottom layer comprises a reactive sputteringprocess.
 7. The method as claimed in claim 4, wherein said oxidationprocess to said surface of said chromium-containing bottom layercomprises an anneal process.
 8. The method as claimed in claim 1,wherein said insulating film has a thickness in the range of 5nanometers to 50 nanometers.
 9. The method as claimed in claim 1,wherein said first etchant comprises a mixture of a phosphoric acid, anitric acid and an acetic acid, where a sum of concentrations of saidnitric acid and said acetic acid is at least 16 percent by weight. 10.The method as claimed in claim 1, further including the step of carryingout a selective dry etching process, in addition to said secondselective wet etching process, for selectively etching saidchromium-containing bottom layer.
 11. The method as claimed in claim 10,further including the step of removing a dry etching gas from a surfaceof said aluminum-containing top layer after said selective dry etchingprocess using said dry etching gas has been completed.
 12. The method asclaimed in claim 1, wherein said chromium-containing bottom layercomprises one of a chromium layer and a chromium alloy layer, and saidaluminum-containing top layer comprises one of an aluminum layer or analuminum alloy layer.
 13. The method as claimed in claim 1, wherein saidelectrically conductive lamination pattern is formed over a substratefor a liquid crystal display panel.
 14. A method of forming anelectrically conductive lamination pattern, said method including thesteps of: forming a chromium-containing bottom layer over a substrate;forming an aluminum-containing top layer over an insulating film, sothat said insulating film separates said aluminum-containing top layerfrom said chromium-containing bottom layer; forming a resist patternover said aluminum-containing top layer; carrying out a first selectivewet etching process for selectively etching said aluminum-containing toplayer with a first etchant and said resist pattern; removing said resistpattern from said aluminum-containing top layer; and carrying out asecond selective wet etching process for selectively etching saidchromium-containing bottom layer with a second etchant and by using, asa mask, said aluminum-containing top layer wet-etched.
 15. The method asclaimed in claim 14, wherein said first etchant comprises a mixture of aphosphoric acid, a nitric acid and an acetic acid, where a sum ofconcentrations of said nitric acid and said acetic acid is at least 16percent by weight.
 16. The method as claimed in claim 14, furtherincluding the step of forming an insulating film on a surface of saidchromium-containing bottom layer before said aluminum-containing toplayer is then formed, so that said second selective wet etching processis carried out in the presence of said insulating film which suppressesa hetero-metal-contact-potential-difference between saidchromium-containing bottom layer and said aluminum-containing top layerduring said second selective wet etching process.
 17. The method asclaimed in claim 16, wherein said insulating film comprises an oxidefilm formed by an oxidation process to said surface of saidchromium-containing bottom layer.
 18. The method as claimed in claim 17,wherein said oxidation process to said surface of saidchromium-containing bottom layer comprises an O₂ plasma process.
 19. Themethod as claimed in claim 17, wherein said oxidation process to saidsurface of said chromium-containing bottom layer comprises a reactivesputtering process.
 20. The method as claimed in claim 17, wherein saidoxidation process to said surface of said chromium-containing bottomlayer comprises an anneal process.
 21. The method as claimed in claim16, wherein said insulating film has a thickness in the range of 5nanometers to 50 nanometers.
 22. The method as claimed in claim 14,further including the step of carrying out a selective dry etchingprocess, in addition to said second selective wet etching process, forselectively etching said chromium-containing bottom layer.
 23. Themethod as claimed in claim 22, further including the step of removing adry etching gas from a surface of said aluminum-containing top layerafter said selective dry etching process using said dry etching gas hasbeen completed.
 24. The method as claimed in claim 14, wherein saidchromium-containing bottom layer comprises one of a chromium layer and achromium alloy layer, and said aluminum-containing top layer comprisesone of an aluminum layer or an aluminum alloy layer.
 25. The method asclaimed in claim 14, wherein said substrate is a thin film transistorsubstrate for a liquid crystal display.